This invention relates to temperature controlled soldering irons and more particularly to an electric soldering iron with improved means for controlling the temperature of the iron.
The well known construction of temperature controlled soldering irons is exemplified by Finch U.S. Pats. Nos. 2,897,335 and 3,699,306 and has a relatively massive iron tip, a heating element and a thermocouple. The thermocouple is attached to the iron tip at a point which is remote from where soldering is performed. The heating element and ends of the wire which connect the element and thermocouple to an external power supply and control circuit are housed in a tubular metal shank which is attached to the iron tip. A wooden or plastic handle is attached to the opposite end portion of the tubular shank.
One deficiency with this construction, that the present invention addresses, is that the temperature of the tip at the point where soldering is performed cannot be instantaneously controlled because of a time lag caused by the separation of the attachment of the thermocouple which senses temperature from the point of soldering.
Another deficiency is the slow warm-up of the tip because of the mass of the soldering tip and heating element. A result of the slow warm-up is that when soldering is not in process, the iron is generally maintained in a heated stand-by condition to avoid delays when soldering is to be done. This is both wasteful of electrical energy and detracts from the utility of battery operated models, because of the current drain on batteries.
Another deficiency with this construction is an undesirably high handle temperature because the iron is maintained in a heated condition and the method of attachment of the handle to the tubular shank.
It is further noteworthy that the new technology of surface mounting components to printed circuit boards and reductions in size and power rating of electronic components has increased the need for an improved temperature controlled soldering iron.
One important feature of the present invention is that a single pair of dissimilar conductors provides a soldering tip, a heating element and a means for directly sensing temperature at the point of soldering of the tip. Thus, complexity is reduced and the separation of the thermocouple attachment from the point of soldering is eliminated. It is needless to say reliability will be improved because of the reduced complexity. Moreover, the present invention provides the further benefits of reductions in size, weight, cost, and warm-up time of temperature controlled soldering irons.
Since the invention substantially reduces warm-up time, it follows that irons which embody the invention may be switched on and off, on an "as-needed" basis without loss of utility. Also, as will be appreciated, the reduced size and weight facilitates the handling and soldering small electronic components.
Another feature of the invention, which in itself is believed novel, is the unique means of attaching the handle which provides the benefit of reduced handle temperature.
The pair of conductors which provide a soldering tip, heating element and temperature sensor are made of dissimilar metals, of the type commonly used for making thermocouples, such as Nichrome and Constantan. One end portion of the connectors are joined together to form a soldering tip and except for the union at the soldering tip, the conductors are separated in a side-by-side arrangement. The other end portions of the conductors are connected to an external A.C. power supply and electronic control circuit.
The dissimilar conductors are mounted in a tubular shank which is attached to a handle by a spider-shaped bracket which reduces heat transfer from the shank to the handle.
The conductors are in series with one another and the secondary winding of a transformer which provides A.C. current for heating the conductors. Transformer current is regulated by a triac in the external control circuit. An "on-off" switch is provided to operate the soldering iron on an "as-needed" basis.
When an A.C. current from the transformer flows through the conductors, the temperature of the conductors is raised and a D.C. voltage is generated by the conductors which is directly proportional to the temperature of the conductors. Since the conductors serve as the soldering tip, the D.C. voltage provides a signal for instantaneously sensing the temperature of the tip. The D.C. voltage is applied to the control circuit where it is amplified and compared against a reference voltage which is pre-selected, by a user, in accordance with a desired soldering temperature. The difference between the D.C. signal and reference voltage is applied to a triac which controls the current supplied by the transformer to the series connected dissimilar conductors.
Further features of the invention along with additional benefits and objects will become apparent by reference to the drawings and ensuing detailed description of the preferred embodiment of the invention which discloses the best mode contemplated in carrying out the invention. The subject matter in which exclusive rights is claimed is set forth in the numbered claims following the detailed description of the invention.